Cryo-thermal process for fracturing rock formations

ABSTRACT

A process for fracturing rock formations is disclosed using cryogenic fluids and exemplified in a process for the secondary recovery of oil wherein the major steps include: establishing a complex of elongated holes arranged in a predetermined geometric pattern which penetrate the oil production formation; injecting pressurized, superheated steam into the holes; fracturing the oil production formation using cryogenic techniques; and recovering the mobilized oil.

L o o a u n O 0 Umted States Patent 1191 1111 3,759,329

Ross Sept. 18, 1973 [54] CRYO-THERMAL PROCESS FOR 3 3,152,651 10/1964Ross..... 175/11 R NG O K FORMATIONS 3,358,763 12/1967 Petty et a1.166/308 X 3,393,741 7/1968 l-lultt etal. 166/308 Inventor: ig Ross,Bronx, 3,396,107 8/1968 Hill 166 308 x 3,412,797 11/1968 Huitt et a1166/308 [731 Assgnee- Scarsdale, 3,664,422 5/1972 Bullen 166/308 [22]1971 FOREIGN PATENTS OR APPLICATIONS 1 PP 148,048 511,768 /1939 GreatBritain 166/272 Related US. Application Data I [63] Continuation-impartof Ser. No. 823,306, May 9, Novosad 1969, pat. 3,581,821 vAttorney-R1chard K. Parsell 52 s. (:1 166/308, 166/302, 166/303, [51] IABSTRACT {51] Int Cl 1 fg gg A process for fracturing rock formations isdisclosed [58] Fie'ld 302 303 using cryogenic fluids and exemplified ina process for 6/272 Z 3 the secondary recovery of oil wherein the majorsteps include: establishing a complexi of elongatedholes ar- [56]References Cited ranged in a predetermined geometric pattern whichpenetrate the oil production formation; injecting pres- UNITED STATESPATENTS surized, superheated steam into the holes; fracturing 895,6128/1908 Baker 166/272X the roduction formation using cryogenic techgniques; and recovering the mobilized oil. oss I 3,108,636 10/1963Peterson 166/308 10 chums, 1 makin Figures CRYOGENIC THERMAL ENERGYGENERATOR FLUID ,INPUT o 1 42 V "7739 it 611 5 7 A 00610511 55134 -cYoGN1c FLUID OUTPUT,

Patented Sept. 18, 1973 I I 3,759,329

3 Sheets-Sheet 1 FIG. I:

SUPERHEATER STEAM GENERATOR I ll INVENTOR SIGMUND L. ROSS Patented Sept.18, 1973 3 Sheets-Sheet 2 FIG. 30

FIG. 3b

.FIG. 2f

FIG. 3c

PRESSURE WELL I FIG. 3f R-$6 PRESSURE WELL I PRESSURE WELLS PRESSURE QWELL I I PRESSURE WELL c? 1 F|G.4

- ATTORNEYS Patented Sept. 18, 1973 3 Sheets-Sheet 3 FIG; 6

CRYOGENQC FLUID INPUT THERMAL ENERGY GENERATOR CONDENSER CRYOGENIC FLUIDOUTPUT INVENTOR SIGMUND L ROSS CRYO-THERMAL PROCESS FOR FRACTURING ROCKFORMATIONS CROSS REFERENCE TO RELATED APPLICATION This application is acontinuation-in-part of my application Ser. No. 823,306 filed May 9,i969 for Cryo- Thermal Process For The Recovery of Oil which resulted inU.S. Pat. No. 3,581,821.

FIELD OF INVENTION This invention relates to the fracturing of rockformations.

BACKGROUND OF THE INVENTION ing, (d) gas injection, and (e) excavationand retorting.

Methods (a) through (d) employ procedures which will force the oil inplace to migrate either directly or by reducing the viscosity of theoil. The latter is particularly important with regard to highly viscousoils.

Steam flooding has been used in conventional techniques to supply forceand to reduce viscosity. The injected steam tends to raise thetemperature of the petroleum reservoir. The resulting thermal expansionof the in-place petroleum in connection with gas pressure created bysteam distillation of a portion of the petroleum forces the oil depositto move or migrate to a relief zone. Usually this relief zone is theinvasion hole drilled into the formation up through which the oil rises.

There are three zones created by conventional steam injection: first, asteam zone near the well bore; second, a hot water condensate zone wherethe steam condenses; and third, a water and condensate zone where thewater and condensate reach the ambient tempera- Another object of thisinvention is to assist in the recovering of oil by the use of cryogenicmethods.

A further object is to provide an oil recovery process which isefficient and economical using selected combinations of the above steps.

In accordance with the invention, a method for recovering oil from aformation containing oil in a nonflowable state comprises establishing acomplex of elongated holes arranged in a predetermined geometric patternwhich penetrate an oil production formation. The method furtherincludesinjecting pressurized, superheated steam into at least one ofthe holes, fracturing the oil production formation using cryogenicfluids v and recovering the mobilized oil.

For a better understanding of the present invention together with otherand further objects thereof, reference is made to the followingdescription taken in' connection with the accompanying drawings, and thescope of the invention will be pointed out in the appended claims.

In the drawings:

FIG. 1 illustrates a partly sectioned vertical view of an arrangementfor providing pressurized, superheated ture of the reservoir. The heatenergy imparted to the ing the cavity walls. This results in excessivecondensation on the cavity walls and increasing difficulty in heatingthe cavity. The long periods required to stage a field using thistechnique also make it uneconomical as well as inefficient.

The present invention obviates many of the disadvantages of theconventional steam flooding operation and provides additional stepswhich make oil recovery techniques, particularly with regard tosecondary oil recovery, highly efficient and economical.

An object of this invention, therefore, is to improve the recovery ofoil using novel thermal techniques.

An additional object is to aid recovery of oil by the use ofgeometrically arranged and spaced hole formations.

steam to a bore hole;

FIG. 2 a-f shows an elevational view of embodiments of a steam jetnozzle for use with this invention;

FIG. 3 kz-f has illustrated plan views of the preferred geometric holearrangements for use with this invention; r FIG. 4 is a plan view of thefive-hole pattern in more detail; v v H FIG.j5 is a vertical sectionalview of the, oil formation using the five-hole arrangement of FIG. 4;and FIG. 6 illustrates a partially schematic and partial plan view ofthe steam stimulation-pressure well technique as implemented.

GENERAL DESCRIPTION OF THE INVENTION Although the following cryo-thermalprocess of secondary oilrecovery and its variations are to .be describedin general terms, it must be recognized that this technique willvv aryaccording to the characteristics of the in-place petroleum as well asthe nature of the formation where the petroleum isfound.

A major feature of the process is the injection of pressurized,superheated steam into a complex of elongated bore holes. Generally thenumber of holes will be ten or less and will be spaced between feetminimum and 600 feet maximum of each otherfrom center to center of theholes. The complex of holesis in specific geometric formation. a

The use of superheated steam provides significant advantages overnon-superheated steam. First, a moderate amount of superheat greatlyincreases the volume of the steam. The quantity of water required for agiven amount of heat energy is therefore greatly reduced. Second,thermal conductivity of superheated steam is less than that of saturatedsteam, therefore, less heat is lost through pipe walls and more heatenergy is delivered to the pay zone Third, considerably more heat may beextracted from superheated steam for the same amount of fuel used.

The high temperature superheated steam is introduced into thehole'complex under very high pressure to create thermal expansion in theoil, to lower the viscosity of the oil, to liberate the hydrocarbongases from the in-place petroleum, and to flash much of the connatewater present in the formation into additional steam. All of the abovecombine to generate a force to mobilize the in-place oil. In addition,pressure is rapidly built up in the hole which densifies the pay zoneimmediately adjacent the hole. The degree of densification of thestimulation well, in that region wherein the heat is being introduced,improves the local thermal conductivity, thus permitting more heatenergy to bring about in-place petroleum migration.

Under certain conditions, the pressurized, superheated steaming alonewill cause the oil adjacent the hole to move into the hole where it iscarried up and out. The pressurized gases, which rise up the hole abovethe point at which the steam is energizing, create a pressuredifferential within the hole which also tends to pull out the oil inplace.

A second feature of the process is the use of a cyrogenically producedoxidizing liquid such as liquid oxygen (LOX) in addition to thepressurized, superheated steam to provide additional heat energy to thepay load. Certain formations have faults or cracks which will tend tosiphon off some of the injected steam, which detrimentally lower the payzone temperature. If this occurs, liquid oxygen may be mechanicallyintroduced into the pay zone. The effect of an oxidizing agent such asliquid oxygen being subjected to intense heat and pressure andcontacting organic combustible material such as grease, oil, tar,asphalt and kerosene is to deflagrate or rapidly oxidize. The materialso exposed will burn fiercely and will raise the temperature of the payzone considerably, as well as the shaft of the elongated hole. The heatgenerated by the LOX oxidation will also flash the connate water in theinterstices of the pay zone into additional steam. secondarily, thedeflagration will effectively contribute to fracturing the pay zoneregion of the formation. To reiterate, the purpose of the LOX is toaccelerate the heat stimulation process. Fracturing may occur as aresult of this high heat energy level by the mechanism of isotropic oranisotropic expansion. After its initial use the LOX will be usedwhenever the bore holes of the stimulation wells drop below thetemperature of the injected superheated steam.

The hot bore hole produced by the superheated, pressurized steam and theLOX injection has further advantageous effects on oil recovery. First,the lighter hydrocarbons become gaseous and expand, which, on risingupward, expand further because of the reduction of ambient pressure.This tends to increase the pressure differential in the hole. Anybubbles of gas present in individual oil droplets tend to expand theoil, further destroying any cohesive property of the oil on sand grainsand other detritus.

In addition, the existence of temperature differentials as well aspressure differentials at different levels in the bore hole effectivelycreate a fractionating distillation column tending to break outadditional chemical elements which may be present in the oil.

It should be emphasized that both pressurized, superheatedsteam and theLOX injection may be applied to all or selected holes of the holecomplex mentioned earlier. This will largely be determined by the natureof the oil in place, the type of formation and the geographical featuresof the terrain.

A third feature of this process is the use of cryogenic freezing ofmoisture or fluid in the pay zone region. This may be accomplished byapplication of a cryogenic fluid to one or a number of the holes ifthere is sufficient moisture in the soil of the pay zone (e.g. more than15 percent moisture content). If the moisture content is not this high,a fluid, preferably water, is injected in the desired hole or holes.Then the cryogenic fluid or solid is inserted which rapidly freezes thewater. Liquid nitrogen is a preferred freezing agent althoughpressurized CO may also be effective.

The fluid in the hole is quick frozen. If it is water, it expands andswells and laterally, and to some extent vertically, displaces the payzone in the region of the hole. The effect of this is to collapse thepores of the formation which squeezes the trapped oil and water in theinterstices of the formation. Additionally, the connate water is frozenand expanded. A third effect is to improve, locally, the thermalconductivity of the pay zone both by freezing and by densiflcation. Theeffect of the swelling in a central well, when coupled with the heat andpressure in adjacent or flanking well is to figuratively put theformation through a wringer and the petroleum literally wrung out. w

The effect of improving local thermal conductivity is important if thereis a desire to directionalizethe heat flow in the pay zone. In additionto extracting the pay zone oil directly from the superheated hole, itmay be desired to use certain of the extreme holes as stimulation holes(i.e.inject the high energy thermal sources there), and other extremeholes, preferably on the other side of the formation, as productionholes (i.e. remove the oil there). The heat energy and pressure willcause migration of the oil from the stimulation holes to the productionholes from which the oil will be removed. If the thermal conductivity ofthe formation were increased in the direction of migration of the oil,it would accelerate the migration process by directing the flow of heatfrom the stimulation holes to the production holes. To-this effect, therapid freezing of a central or pressure hole between stimulation andproduction holeswill be advantageous.

It may be desirable to use pressurized nitrogen gas in addition to andin conjunction with the quick-freezing of the pressure well to createadditional fracturing and better mobilization of oil.

The cryogenic technique may be used at any stage of the overallsecondary oil recovery process as seems ad'- vantageous.

DETAILED DESCRIPTION OF The INVENTION A more detailed discussion ofspecific embodiments of the invention will now be described.

Referring first to FIG. 1, a particular arrangement for injecting thepressurized steam is shown. A water pump 10 drawswater through a suctionline and supplies the water to a steam generator 1 l. The steam outputis then supplied to a superheater 12 which provides theadditional heatenergy necessary to superheat the steam to the desired temperature. Thepressure of the superheated steam will be controlled by the rate ofconversion of water to superheated steam. The pump 10, steam generatorll and superheater 12 may be provided on a mobile unit. The pressurized,superheated steam is directed through a flexible meta] hose 13 which isguided by an overhead support 14. The metal superheated steam line 13,preferably created from stainless steel, is connected to a steam lance15 which has a head 16 to which a plurality of nozzles 23 is attached.The steam lance 15 is inserted in a pre-drilled bore hole in tightformations or may be used to bore its own hole by virtue of the highpressure coming from the lance head 16. The diameter of the bore holemust be such as to accept a minimum 54 inch casing 19. The casing 19must accommodate the steam lance l5 and the oil take-up pipe 20. Pipe 20has attached to it pressure 21 and temperature 22 indicators which helpto determine the nature of the-bore hole and pay zone and theappropriate moment for oil removal. Pipe 20 is connected to storagetanks (not shown).

Although the superheated steam injection is similar whether oil is to beremoved from the same hole or will be removed from a different hole,FIG. 1 is illustrative of,oi removal from the steam-stimulated hole.

The 6 is shown in more detail in FIG. 2 a-f.

FIG. 2a shows a cross section of a jet nozzle 23 which is the heart ofhead 16. The nozzle 23 is shown to have an interior Venturi arrangementfor optimizing the pressure of the steam. FIGS. 2b-2fshow variousarrangements and orientations of the nozzle as it is attached to head16. In FIG. 2b, a single nozzle 23 is downwardly directed. FIG. 2c showsa single nozzle at 90 to the vertical'attached using a rounded elbow.FIG. 2d illustrates a straight tee arrangement for achieving a 90 nozzleattachment which has the capability of adding an additionaldownward-directed nozzle. FIG. 2e indicates just such a connection bytwo 90 oriented'nozzles attached to steam head 16.

The preferred arrangement is 2f. This arrangement has five nozzles 23connected to the steam head 16. One nozzle 23a is directed verticallydownward and the others, 23b, 23c, 23dand 23e, are arrangedconcentrically and symmetrically in a horizontal plane. Otherarrangements of nozzles 23 may also prove advantageous.

The steam slams out of jet nozzles 23 at a speed between a mach 2andmach 4. The steam lance may thus be used to drill its own hole in looseformations.

As the steam pipe starts down the bore hole, it jets out acontinuousflow of steam. The only time steaming is interruPted is whenadditional lengths of pipe are added. As the steam lance enters the payzone, the descent of the lance is preferably interrupted and the regionof the pay zone will be subjected to a period of steaming forapproximately minutes. Then the lance will continue its descent,stopping every 20 feet in soft formations and 10 feet in tightformations. The descent of the lance will continue until the bottom ofthe'pay zone is reached. At this point, the lance will be raised some 3feet and steaming will continue and will'not be interrupted until thetemperature of the bore hole drops belowa certain level (e.g. 250F. lessthan the injected steam) at which point some other step such as LOXapplication will be used or the process discontinued as to this pay zonearea.

Typically, in the initial steaming operation, if the temperature of thebore falls below this prescribed level, the injection of liquid oxygenwill then commence. If the bore hole is large enough, the LOX willmerely be dropped down the hole at intermittent intervals. In the eventthe bore hole is not large enough to contain both thesteam line and theLOX container, steam injection will be interrupted and the steam linewill be valved off, disconnected and removed. Then glass containers,about one liter in volume, filled with- LOX and stoppered with a gasescapetube in place are intermittently dropped down the hole. Thecontainers will burst open, striking the bottom of the hole andspattering the LOX which had not escaped through the gas relief tubearound the region of the hole. The LOX, in coming into contact with theheated petroleum flashes into flame, developing intense heat.

In certain instances, this high localized heat may cause thesilicarportion of the sands in the pay zone to fuse. In. this event,methyl alcohol, chilled to an appro priate temperature, to minus F. forexample, and under a predetermined pressure, 300 psig. pressure forexample, is released through a pipe down the bore hole to impact andsplatter on the extremely hot fused silica. Thermal shock follows whichshatters the silica,

thereby creating a path for subsequently applied superheated steam.

Referring now to FIG. 3, shown are preferred arrangements of geometrichole formations for three to 10 holes. The number of holes will varydepending on the size and nature of the formation. The holes are to beused in applying the superheated steam and LOX steps of the inventionand the appropriate holes for directionalizing the oil flow using thepressure well technique are indicated as well.

Regarding the pressure hole or well step, reference is now made to FIG.4. In that figure a particular arrangement of five wells is shown toindicate the operation of the pressure well technique and the limits ofthe regions of influence of applied thermal energy.

The'first two wells 25, 26, stimulation wells, are drilled in line. Thethird well 27 is spaced equidistant between the first two 25, 26 and atthesame distance from the first two along a line normal to wells 25, and26. Wells 28 and 29 are located-similarto wells 25 .and 26 andequidistant from well 27 along a line normal to wells 28 and 29. Thecenter-well is called the pressure well, while wells 28 and 29 arecalled the production wells. The approximate regions of influence. ofeach well are shown by the larger circles surrounding each of the wells.V i v Well 27 is typically to be filled with water to a point some 10feet above the payzone of the formation. Tanks containing liquidnitrogen are lowered into the water. The liquid nitrogen tankspreferably have a quick-opening device to be controlled from the surfacewhich rapidly expels the liquidnitrogen into the water. The water thenquick-freezes and fractures the formation as previously described Analternate approach is to circulate either liquid nitrogen or anothersuitable cryogenic fluid through a closed pipe in the bore hole. It maybe desireableto use pressurized nitrogen gas in conjunction with theice-creating pressures to-provide additional pressures to the pay zoneto further fracture the formation and mobilize the oil.- I

The pay zone in thevicinity of pressure well27 is fractured whichsqueezes out some trapped oil and directionalizes the flowof heat fromthe stimulation wells 25 and 26 to the production wells. The in-placepetroleum will follow the least resistant thermal path and the newlycreated fissures from the stimulation wells 26 face is closed by acollar. In the collar is welded a threaded pipe nipple.

The purpose of the nipple is to regulate the pressure build-up in thestimulation wells; in addition, it permits the attachment of a secondaryheat line which may convey escaping heat energy into the bore holes ofthe production wells tofacilitate oil flow as mentioned above.

Referring now to FIG. 5, the injection profile of the five-well approachusing the center pressure well is shown, including the direction ofheat-flow. Also indicated are the limits of the local primary heatinfluence. Note that the depths of the wells are sloped toward theproduction wells to take advantage of natural drainage.

A preferred embodiment for implementing the pressure well technique isshown for a five-well arrangement in FIG. 6. A thermal energy generator30 supplies the pressurized, superheated steam to a main steam line 31.The main steam line 31 is connected to the stimulation wells 32 and 33which would typically be closed by a collar with an attached nipple aspreviously mentioned. Secondary heat lines 37 and 38 are attached to thenipples in the stimulation collars and connect to the production wells34 and 35. The output oil lines from the production wells connect toline 44 which is brought to oil storage tanks 45. The gaseous portionsof the'production well output are forced out of the storage tanks 45 asthe tanks fill up. The gas enters gas vent line 42 or auxiliary gas feedline 41. If the gas is transmitted through gas vent line 42, it iscondensed in gas condenser 39 by the circulation of cryogenic fluids.The distilled gases are collected in distillate sotrage tank 40. Thedistillate may be drawn off by output line 43. The auxiliary gas feedline 41 disposes of the gas in some other predetermined manner. Thus,all portions of the oil well output are collected and may be used.

Extensions to a second well complex are shown by wells 47, 48 and '49.ln'this case, well 47 will be the pressure well and wells 48 and 49 willbe the production wells. Similarly, a third and additioncomplexes may beadded by adding three additional wells, e.g. 50, 51, 52, to the existingcomplex.

It should also be noted that if a fracturezone exists in the formation,it may not be necessary to use a center pressure well. Also, it may notprove necessary to directionalize the heat flow in an existingformation. What will determine if all or part of the above process isused are the following general criteria: (1) permeability of theformation pay zone; (2) porosity of the pay zone; (3) the percentage ofoil, water or gas in place; (4) reservoir pressure (if any); type offormation of the pay zone; and (6) the Terrastatic pressure confiningthe pay zone.

.The following are examples of how the invention may be used in aparticular oil-bearing formation. The examples were chosen to indicatemulti-step application of the invention.

EXAMPLE 1 Conditions: Pay zone formation is located on the forward slopeof an anticline. Depth is 1672 feet down. Permeability of the formationis 46 millidarcies. Percentage of porosity of the formation is 34.4. Ofthis 34.4%, 27% is oil and 56% is water, the rest being gas. A.P.A.gravity is 24.

Process: Construct the five-well complex as shown in FIG. 4. The wellsare generally drilled to the depth shown in FIG. 5 taking advantage ofnatural drainage. Fill the center well with water from the bottom to apoint 10 feet above the pay zone or 10 feet up into the rock masscapping the oil sands. Lower tanks filled with liquid nitrogen into thewater and quickly release the liquid nitrogen to rapidly freeze thewater, thereby trapping the nitrogen tanks in place.

Apply the superheated steam to the bore holes of both stimulation wells.Position the jet nozzles of the steam line approximately one inch fromthe face of the formation at the bottom of the pay zone. The nozzle isdirected horizontally and tangent to the radius of influence ofdensification peripheral to the pressure well. Inject superheated steamat 950 psig and 950F. into the stimulation wells. The effective rate ofsteam flow per second is l b lbs. (by weight).

Continue steaming for 24 hours, with a collar closure including pipenipples around the bore holes.

After 24 hours, disconnect the steam line and remove it from the borehole.

Drop liquid oxygen in liter glass containers down the bore hole at therate of one every 15 minutes. Continue for 1 hour. After LOXapplication; reconnect the steam lines and continue steaming for 7 days.Resume LOX treatment during the 7 days only'if the bore hole temperaturedrops below the temperature of the steam.

After the seven days test the trapped tanks in the pressure well todetermine whether they can be hauled up. (If they can, it means thatsufficient heat has migrated to the center well and wholly or partiallymelted the ice.) After hauling up the tanks, check the water in the borehole for gas infusion, for oilpresence and for temperature. If thetemperature is substantially above freezing, stop steaming, disconnectthe steam lines and begin dropping LOX at 15-minute intervals for 2hours in the stimulation wells. Reconnect the steam lines and resumesteamingfor another seven days. During this second 7-day intervalcontinue checking the pressure well every 6 hours for temperature, oilshow and gas infusion.

Once the entrapped tanks are removable and there are oil and/or gasinfusions, it means the heat energy is migrating effectively. When thetemperature of the center well reaches half that of the stimulationwells, the producing wells are quick-frozen to improve the thermalconductivity of that area by the techniques already described. 7

if the oil in the pay zone is more viscous between the pressure well andthe producing well, than between stimulation well and pressure well,apply superheated steam to the production wells using steam lines andjet nozzles for a period of two hours'at the same pressure andtemperature as that existing in the stimulation wells.

If additionally necessary, remove steam lines, pump in water under highpressure of an amount in gallons equal to thepay zone depth and followwith liquid nitrogen to improve the directionalized heat flow toward theproduction wells.

Eventually the oil will begin to surge up the production wells.

EXAMPLE 2 Given the same conditions as Example 1 and following similarprocedures, if at the end of the second 7-day period the middle welltemperature has not risen substantially to at least half the temperatureof the stimulation wells it means that the migrating heat energy hasbeen stopped by a permeability barrier or fault.

Then steam or pump the water out of the center well. Connect a secondarysteam line to the pipe nipple on the stimulation wells and insert in thecenter well. After three hours remoVe the steam line and pour some crudeoil down the well so that it covers the pay zone but does not penetratedue to its viscosity. Drop LOX down the center bore hole at -minuteintervals for an hour. Then an insulated line is used to apply methylalcohol chilled to a temperature of approximately 60F. and forced underpressure (300 psig) down the center hole. The purpose, of course, is toapply thermal shock to fracture the formation and break through thefault. This procedure may be repeatd if necessary.

Eventually, oil or gas infusion will be visible in the center hole andthe process described in Example 1 should be continued.

EXAMPLE 3 In a syncline geographic situation (trough), the generalfive-well implementation will use four stimulation wells and a centerproducing well .without a central pressure well. The general procuesuresof Example 1 should then be followed.

As indicated by the foregoing examples, the exact process depends on thenature of the terrain and the response of the pay zone to the appliedsteps.

While general reference has been made to the use of the presentinvention with regard to secondary recovery of oil, no limitationprecludes use of any or all of the steps of this invention to primaryoil recovery as well.

The utilization of this invention in the fracturing of a rock formationis characterized by flash freezing accomplished by the release of acryogenic liquid'in thermal association therewith. The employment of acryogenic liquid is of critical importance. Heretofore refrigeration hasbeen employed to freeze an earth or rock formation for such purposes asstabilization of the formation or preventing the percolation of a liquidtherethrough. However, mere freezing has been found to be ineffective inaccomplishing a useful amount of fracturing. This ineffectualness in theaccomplishment of fracturing as compared with the fracturing that isobtainable in the practice of the invention by the employment of acryogenic fluid is due to various causes. Thus, if the formation ismerely subjected to the action of a refrigerant at a rate usuallyassociated with freezing accomplished by refrigeration, the cooling offand freezing are more gradual. Under such conditions the ice formationtends to be oriented laterally to a lesserextent with resultantlessening of ting of directionalized expansive forces. There also is atendency for water to migrate. Moreover, the expansive forces areapplied more gradually and with less tendency to fracture. When, on theother hand, a cryogenic fluid is employed in intimate contact with wateror with a rock formation containing water, the water that is present isfrozen extremely rapidly, namely, is flash frozen as this term is knownin the art. Under such conditions the crystal formation is such that theexpansion forces are directed laterally to a much greater degree.Moreover, the expansion forces are applied with suddenness that is akinto a fracturing blow as distinguished from a gradually applied pressure.in addition, there is less tendency for the water to 'little fracturingeffectiveness.

migrate and full advantage is taken of its presence at the points wherefracturing is induced.

A cryogenic liquid, as this term is used herein, is one which remainsliquid at a temperature of minus 298F. or less. The cryogenic liquid, asinitially furnished, is under sufficient pressure to maintain it in theliquid state under conditions of normal temperature. When the pressureis released the expansion and evaporation produce extremely lowtemperatures virtually instantaneously, and water and rockin theadjacent area are reduced very quickly to a temperature which typicallymay be of the order of minus 60F. with concomitant conversion of thewater to ice so suddently that fracturing of a rock formation isaccomplished very effectively as the result of the flash expansion involume upon the transformation of the water to ice.

As stated hereinabove, the fracturing may be caused solely by watercontained in a rock formation so long as the water content'is at leastabout 15 percent by volume. In such case when the amount of water isabove 15 percent by volume, the flash freezing occurs in the rockformation adjacent the released cryogenic liquid, which flash freezingeffectively fractures the adjacent formation. If the formationthereafter is permitted to thaw and additional water is taken up by theformation which has been rendered more receptive thereto by the initialfracturing, the amount and extent of the zone of fracture may be greatlyaugmented by a second release of a cryogenic liquid which causes flashfreezing of the water in the formation.

As stated hereinabove, maximum fracturing effectiveness is obtainedaccording to this invention when free water is caused to be present inthe cavity in addition to any water naturally present in the formation.By the addition of free water, the amount of water in such intersticesas there may be in the formation is increased to a maximum withresultant enhancement of the fracturing effect. Moreover, the body offree water, such as that in an 8-inch diameter oil well bore in theoilbearing zone, itself applies great lateral forces to the walls of thebore with resulting fracturing effect. As stated above, ice tends toexpand laterally under conditions of .flash freezing. The necessity forflash freezing by the employment of a cryogenic liquid is especiallywell illustrated when free water is present in the bore of the oil well.When flash freezing is caused to occur, the expansion not only is suddenbut most of it is lateral so as to fracture the walls of the bore. If,on the other hand, the water is gradually frozen as by the use of arefrigerant the ice as it is fonned tends to accommodate itself to theconfining walls of the bore with the result that most of the expansionis upwardly and there is very The enhancement of fracturing effect byrepetition is particularly applicable when there is free water that isflash frozen in a cavity in the rock formation. After the initialfracture produced by flash freezing, a quantity of the free water may beremelted. For example, when water in the bore of an oil well has beenflash frozen in the oil-producing zone, the ice in the upper portion ofthe oil-producing zone, e.g. to an extent of 5 to 10 feet, may bemelted. The. resulting water then is permitted to percolate into therock formation which has been opened up by the initial fracturing.Upon'again flash freezing the water in the bore, the fracturing becomeshighly effective so as to extend laterally a greater distance ascompared with the initial fracture.

By the employment of this invention, fracturing of rock formations suchas those encountered in the oilbearing zone of an oil well can beaccomplished in greater amount both as to degree and lateral extent thanthat which is believed to have been possible by prior expedients.

As disclosed hereinabove, the release of the cryogenic liquid from thecompressed state should be accomplished in as close proximity aspossible to the zone in which it is desired to induce fracturing. Thismay be accomplished by the placing of a container for the pressurizedcryogenic liquid in the desired proximate posi-v tion and releasing itby opening a valve which quickly releases the pressurized liquid so asto rapidly become chilled and cooled to temperatures much below thefreezing point of water. Alternatively, the pressurized cryogenic liquidcan be directed from a container therefor to the desired locationthrough a line having an outlet, ordinarily controlled by a valve,through which the cryogenic liquid may be released.

Fracturing induced by flash freezing according to this invention may beutilized wherever the fracturing of a rock formation is desired. Thus,it may be employed in. mining which may be either the open pit type orunderground. ln such case penetration into the rock formation ordinarilywould be of a much lesser order as regards depth of penetration anddiameter of the drilled hole. However, the principle is the same asregards fracturing by flash freezing induced by release of a pressurizedcryogenic liquid. In such an operation the flash freezing may be causedto occur at substantially the same time in a plurality of cavities in.proximate spaced relation to each other as, for example, in connectionwith bench drilling. The invention has similar applicability inquarrying. It also has other applications as in tunnel driving, shaftdrilling and boulder breaking.

By plugging a cavity containing free water the fracturing effect can beenhanced. Moreover, by anchoring a plug both below and above a zonewhere fracturing is desired the fracturing can be largely localized inthe desired zone as well as rendered more effective in the desired zone.In applications such as these a container for the cryogenic liquid canbe put in place at the desired location and a release valve therefor canbe actuated by electrical circuit means passing through one of theplugs.

Another expedient for augmenting the effectiveness of the fracturing isthat of undercutting the entrance to a cavity so that the inlet of thecavity has a smaller cross section than the cavity wherein the cryogenicliquid is released. For example, the bore of an oil well may be enlargedin the oil-producing zone of the rock formation by the employment of anexpansion drill.

Liquid nitrogen is the preferred cryogenic liquid because of itsinertness and likewise because of the extremely low temperaturesobtainable upon its release. Nitrogen is liquid at temperatures fromminus 321F. to minus 345F. it also is relatively economical to employ.Oxygen remains a liquid at temperatures of minus 298F. and lower andalso is a cryogenic liquid that may be employed in the practice of thisinvention. However, care has to be exercised in its use in the presenceof a combustible material. There are other cryogenic liquids but forreasons such as cost or hazard they are less practical to use in acommercial operation.

This invention has been illustrated in connection with an oil recoveryoperation wherein fracturing is accomplished by the release of liquidnitrogen in a well so as to cause water to be flash frozen to a levelthat is somewhat above the oil-producing zone. In preferred practice ofthis invention this is accomplished in increments. For example, enoughliquid nitrogen is introduced into the bore of the well to flash freezean amount of water in the bore that fills the bore to a distance ofabout 5 feet at the lowermost portion of the oil-bearing zone. Thevolume of water in this S-foot zone of the bore in the case of a boreabout 8 inches in diameter, for example, is approximately 13 gallons andflash freezing with lowering of the temperature to approximately minus20F. may be accomplished by the release of 20 gallons of liquid nitrogenfrom a container that has been lowered into the bore to positionimmediately above the zone to be flash frozen and that is adapted torelease the liquid nitrogen so as to come in intimate contact with thewater in the zone and cause to be flash frozen. This operation may thenbe repeated in increments of approximately 5 feet each throughout theextent of the oil-bearing zone, for example approximately 40 feet, andpreferably in an additional 5 feet above, the oil-bearing zone. Shorteror longer increments also may be used. Moreover, the water in the regionof the entire oil-bearing zone may be flash frozen in a single step.

While the preferred practice of secondary oil recovery has beendescribed hereinabove wherein superheated steam is injected into a wellthat is adjoining the well in which fracturing occurs, it also is withinthis invention to effect cryothermal fracturing as aforesaid, permit therock formation in the region of the oilbearing zone to thaw out andthereafter inject superheated steam into the well to stimulate flow ofoil into it so that it may be recovered.

The use of liquid nitrogen in the practice of this invention is to bedistinguished from the use of liquid nitrogen or any other cryogenicfluid in the manner disclosed in my U.S. Pat. No. 3,152,651 according towhich a cryogenic liquid is introduced into contact with rock which hasbeen heated 'to a high temperature by means of superheated steam andwhich, therefore, is relatively dry, with the result that the rock issubjected to internal thermal stresses which embrittle it and cause itto fall apart rather than being fractured by the flat freezing of water.The present invention is directed to the surprising fracturingeffectiveness of the flash freezing of water accomplished by a cryogenicliquid as compared with mere freezing as by exposure to subfreezingweather or by being subjected to conventional refrigeration techniques.

While there have been described what are considered to be the preferredembodiments of this invention, it will be obvious to those skilled inthe art that various changes and modifications may be made thereinwithout departing from the invention and it is, therefore, aimed tocover all such changes and modifications as fall within the true spiritand scope of the invention.

I claim:

l. A method of fracturing a rock formation which comprises flashfreezing of water by the release of a pressurized, cryogenic liquid soas to come in intimate contact therewith while said water is confinedfor imposing fracturing pressure on said formation concomitantly withits flash expansion in volume upon transformation into ice. j

2. A method according to claim 1 wherein said cryogenic liquid is liquidnitrogen.

3. A method according to claim 1 wherein the water that is flash frozencomprises water which occurs in the interstices of the rock formation.

4. A method according to claim 1 wherein a hole is made into the rockformation and the pressurized cryogenic liquid is released in the hole.

5. A method according to claim 4 wherein water is introduced into thehole so as to occur as free water therein and wherein said free water isflash frozen by said release of a pressurized cryogenic liquid.

6. A method according to claim 4 wherein said hole is made'in anoil-bearing zone of a rock formation and said cryogenic liquid isreleased in said zone with concomitant fracturing of said zone.

7. A method according to claim 6 wherein the fracturing of the rockformation in the oil-bearing zone is followed by the introduction ofsuperheated steam which stimulates flow of oil into said hole.

8. A method according to claim 4 wherein a container having cryogenicliquid therein is introduced into the hole and the cryogenic liquid isquickly released therefrom.

9. A method according to claim 4 wherein a plug is anchored into thehole and the cryogenic liquid is released in the region ofsaid holeconfined by said plug.

10. A method according to claim 1 wherein the water in the rockformation is melted after the initial fractur ing of the formation,additional water is added in the zone of initial fracture, and thefracturing step is repeated at the zone of initial fracture.

1. A method of fracturing a rock formation which comprises flashfreezing of water by the release of a pressurized, cryogenic liquid soas to come in intimate contact therewith while said water is confinedfor imposing fracturing pressure on said formation concomitantly withits flash expansion in volume upon transformation into ice.
 2. A methodaccording to claim 1 wherein said cryogenic liquid is liquid nitrogen.3. A method according to claim 1 wherein the water that is flash frozencomprises water which occurs in the interstices of the rock formation.4. A method according to claim 1 wherein a hole is made into the rockformation and the pressurized cryogenic liquid is released in the hole.5. A method according to claim 4 wherein water is introduced into thehole so as to occur as free water therein and wherein said free water isflash frozen by said release of a pressurized cryogenic liquid.
 6. Amethod according to claim 4 wherein said hole is made in an oil-bearingzone of a rock formation and said cryogenic liquid is released in saidzone with concomitant fracturing of said zone.
 7. A method according toclaim 6 wherein the fracturing of the rock formation in the oil-bearingzone is followed by the introduction of superheated steam whichstimulates flow of oil into said hole.
 8. A method according to claim 4wherein a container having cryoGenic liquid therein is introduced intothe hole and the cryogenic liquid is quickly released therefrom.
 9. Amethod according to claim 4 wherein a plug is anchored into the hole andthe cryogenic liquid is released in the region of said hole confined bysaid plug.
 10. A method according to claim 1 wherein the water in therock formation is melted after the initial fracturing of the formation,additional water is added in the zone of initial fracture, and thefracturing step is repeated at the zone of initial fracture.